Computer program product to provide bus bar burst communications for an automated data storage library

CROSS REFERENCE TO RELATED APPLICATION

0001The present Application is a Divisional Application of parent application Ser. No. 11/260,933, filed Oct. 27, 2005 now U.S. Pat. No. 7,522,373.

FIELD OF THE INVENTION

0002This invention relates to automated data storage libraries and, more particularly, to communication with the robot accessor of the automated data storage library.

BACKGROUND OF THE INVENTION

0003Automated data storage libraries provide access to data storage cartridges which are typically stored in storage shelves and accessed by a robot accessor having a picker configured to access and deliver data storage cartridges to and from storage shelves and one or more data storage drives. The robot accessor typically moves back and forth among the storage shelves and data storage drives, and positions the picker at the desired storage shelf or data storage drive. Communication is provided to the robot accessor, for example, as commands or signals to make the desired moves, or as address information so that a processor of the robot can determine the desired moves. Additionally, a detector may be mounted on the robot accessor or picker to read information from the shelves, markers within the library, and/or from labels on the data storage cartridges.

0004Communication with the robot accessor is typically made via a flexible cable which unwinds and winds in accordance with the movement of the robot accessor. The flexible cable has certain disadvantages including the possibility of breakage, difficulty in turning corners or crossing aisle intersections, and the need to replace the cable when the library is expanded. Other techniques include wireless radio and infrared communications. Radio poses security and interference risks, while infrared or other optical means can have interference and line-of-sight concerns.

SUMMARY OF THE INVENTION

0005Automated data storage libraries, robot communication systems, and computer program products are provided.

0006In one embodiment, an automated data storage library comprises a plurality of storage shelves, at least one data storage drive, a bus bar, a library communication interface configured to communicate with the bus bar, and a robot accessor. The robot accessor comprises a picker configured to access and deliver data storage cartridges to and from the storage shelves and the data storage drive(s), a drive system configured to move the robot accessor and to position the picker, at least such that the picker may be positioned to access and deliver the data storage cartridge(s), an accessor communication interface, a bus bar relay configured to engage and disengage the bus bar; and a robot control configured to operate the drive system to move the robot accessor, to operate the picker, to operate the bus bar relay to engage the bus bar when the robot accessor is stationary, and to operate the accessor communication interface to provide communication capability with the library communication interface via the bus bar relay and the bus bar when the bus bar relay engages the bus bar.

0007In a further embodiment, the automated data storage library additionally comprises a second communication system between the robot accessor and the automated data storage library, the second communication system operable at least when the robot accessor is moving.

0008In another embodiment, the second communication system is a low bandwidth communication system as compared to communication bandwidth between the accessor interface and the library communication interface via the bus bar relay and the bus bar.

0009In still another embodiment, the second communication system comprises an optical communication system.

0010In a still further embodiment, the second communication system comprises an RF communication system.

0011In another embodiment, the second communication system comprises a roller and bus communication system.

0012In still another embodiment, the second communication system comprises a brush and bus communication system.

0013In a further embodiment, the robot control is additionally configured to stop the robot accessor if, while the bus bar relay is disengaged, communication of the second communication system is lost for a predetermined threshold.

0014In another embodiment, a power supply is configured to supply power to the bus bar, and a power storage system of the robot accessor is configured to receive power via the bus bar relay when it engages the bus bar. Thus both communications and power may be provided via the bus bar and bus bar relay.

0015In a further embodiment, the robot control is configured to determine if the bus bar relay engages the bus bar and, if so, to signal the engagement via the accessor communication interface, e.g. so the power supply may be activated.

0016In another embodiment, a computer program product is configured to operate a programmable computer processor of a robot accessor of an automated data storage library, and comprises computer program code configured to operate the programmable computer processor to operate a drive system to move the robot accessor, to operate a bus bar relay to engage a bus bar of the automated data storage library when the robot accessor is stationary, and to disengage the bus bar of the automated data storage library when the robot accessor is moving; and to operate an accessor communication interface to provide communication capability over the bus bar relay and the bus bar when the bus bar relay engages the bus bar.

0017In a further embodiment, the computer program product computer program code is configured to operate the programmable computer processor to operate a second communication system of the robot accessor at least when the robot accessor is moving.

0018In another embodiment, the computer program product computer program code is configured to operate the programmable computer processor to operate the second communication system in a low bandwidth mode as compared to communication bandwidth of the accessor interface.

0019In still another embodiment, the computer program product computer program code is configured to operate the programmable computer processor to stop the robot accessor if, while the bus bar relay is disengaged, communication of the second communication system is lost for a predetermined threshold.

0020For a fuller understanding of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

0021<figref idref="DRAWINGS">FIG. 1</figref> is an isometric illustration of an automated data storage library employing an embodiment of the present invention;

0022<figref idref="DRAWINGS">FIGS. 2A and 2B</figref> are diagrammatic illustrations of an embodiment of a bus bar relay of the automated data storage library of <figref idref="DRAWINGS">FIG. 1</figref> respectively engaging and disengaging a bus bar in accordance with the present invention;

0023<figref idref="DRAWINGS">FIG. 3</figref> is a block diagrammatic illustration of an embodiment of the communications systems for the robot accessor in the automated data storage library of <figref idref="DRAWINGS">FIG. 1</figref>;

0024<figref idref="DRAWINGS">FIG. 4</figref> is a diagrammatic illustration of an optical communication system employed in one embodiment of the present invention in the communications system of <figref idref="DRAWINGS">FIG. 3</figref>;

0025<figref idref="DRAWINGS">FIG. 5</figref> is a diagrammatic illustration of a roller and bus communication system employed in one embodiment of the present invention in the communications system of <figref idref="DRAWINGS">FIG. 3</figref>; and

0026<figref idref="DRAWINGS">FIG. 6</figref> is a diagrammatic illustration of a brush and bus communication system employed in one embodiment of the present invention in the communications system of <figref idref="DRAWINGS">FIG. 3</figref>.

DETAILED DESCRIPTION OF THE INVENTION

0027This invention is described in preferred embodiments in the following description with reference to the Figures, in which like numbers represent the same or similar elements. While this invention is described in terms of the best mode for achieving this invention's objectives, it will be appreciated by those skilled in the art that variations may be accomplished in view of these teachings without deviating from the spirit or scope of the invention.

0028Referring to <figref idref="DRAWINGS">FIG. 1</figref>, an automated data storage library <b>10</b> is configured in accordance with an embodiment of the present invention with a robot accessor <b>18</b> to access data storage cartridges stored in a plurality of storage shelves <b>16</b>. The library <b>10</b> also comprises one or more data storage drives <b>15</b> which read and/or write data with respect to the data storage cartridges. As one example, the data storage cartridges may comprise magnetic tape cartridges, and the data storage drives <b>15</b> may comprise magnetic tape drives. Other types of removable media drives and cartridges may comprise magnetic media, such as hard disks, floppy disks, or any other type of magnetic media as is known to those of skill in the art. In addition, the removable media drives and cartridges may comprise optical media such as CD (Compact Disk), DVD (Digital Versatile Disk), optical tape, or any other optical media as is known to those of skill in the art. Still further, the removable media drives and cartridges may comprise electronic media such as CF (CompactFlash), SD (Secure Digital), xD (xD-Picture), Memory Stick, MMC (MultiMedia Card), MEMS (Micro-ElectroMechanical Systems) based storage, MRAM (Magnetoresistive Random Access Memory) or any other electronic media as is known to those of skill in the art.

0029The robot accessor <b>18</b> comprises a picker <b>20</b> configured to access and deliver data storage cartridges to and from the storage shelves <b>16</b> and the data storage drive(s) <b>15</b>, and a drive system configured to move the robot accessor and to position the picker, at least such that the picker may be positioned to access and deliver the data storage cartridge(s). In the illustrated example, the drive system comprises a carriage <b>24</b> guided on a lower track <b>26</b> and on an upper track to move the carriage, and, hence picker <b>20</b>, horizontally. The picker <b>20</b> is movable in the vertical direction to access the storage shelves and data storage drives.

0030An accessor sensor <b>22</b>, such as an LED (Light Emitting Diode) emitter/detector, a bar code scanner, camera, and/or other type of reading system, such as a smart card reader, RFID (Radio Frequency Identification), or similar system, may be mounted on the picker <b>20</b>, to “read” identifying information about the data storage cartridges.

0031The automated data storage library <b>10</b> may also comprise one or more operator panels <b>23</b> or other user interface, such as a web-based interface, which allows a user to interact with the library.

0032The automated data storage library may further comprise additional frames, and the track <b>26</b> may continue into the additional frames. In addition, the library may also comprise a second robot accessor, similar to the robot accessor <b>18</b>. In one example, in the event of a failure or other unavailability of the robot accessor <b>18</b>, or its picker <b>20</b>, etc., the second robot accessor takes over.

0033An example of a data storage library which may implement the present invention is the IBM® 3584 UltraScalable® Tape Library.

0034Referring additionally to <figref idref="DRAWINGS">FIGS. 2A</figref>, <b>2</b>B and <b>3</b>, the robot accessor <b>18</b> is provided with a bus bar relay <b>27</b> to provide burst communications when the robot accessor is stationary. Herein, a “stationary” robot accessor refers to motion as it relates to the bus bar <b>28</b>, <b>29</b> of <figref idref="DRAWINGS">FIGS. 1</figref>, <b>2</b> and <b>3</b>. In addition, “stationary” may refer to some amount of motion in that the accessor motion may be decelerating during engagement of the bus bar relay and may be accelerating during disengagement of the bus bar relay. The robot accessor may be stationary when there are no host commands to process. In one embodiment, host commands are received by one or more library controllers and then the commands are either forwarded to the robot accessor, or other commands or signals are sent to the robot accessor to provide the necessary cartridge movement. In addition, the robot accessor may be stationary during a cartridge put or get operation to/from a data storage drive <b>15</b> or to/from a storage slot. The robot accessor may need to be stationary during these actions to prevent damage to components of the accessor. Still further, the robot accessor may be stationary due to a failure of the robot accessor, or if the robot accessor runs out of power, as will be discussed. The bus bar relay <b>27</b> is configured to engage and disengage a bus bar <b>28</b>, <b>29</b> of the library. The bus bar <b>28</b> may comprise any suitable material for carrying communication signals and is arranged generally parallel to the direction of motion of the robot accessor. In the illustrated embodiment, the bus bar <b>28</b> comprises a communication connection, and bus bar <b>29</b> is grounded <b>32</b>. Alternatively, rather than grounding bus bar <b>29</b>, bus bar <b>28</b>, <b>29</b> may comprise a differential communication pair. Still further, there may be only one half <b>28</b> of bus bar <b>28</b>, <b>29</b> and the ground connection may be provided through the contact of other metal parts of the library/accessor system. Still further, there may be more than two connections. In this case, additional connections may be provided for redundancy, for multiple communication channels, etc. Herein, “bus bar” refers to a temporary contact point for providing communication to an accessor, and “bus bar relay” refers to a mechanism for providing the temporary contact to the bus bar.

0035The automated data storage library <b>10</b> is part of a data storage system in which commands and data are provided from one or more hosts <b>31</b> via one or more external interfaces <b>32</b>, and the library executes the commands and provides responses and requested data to the hosts <b>31</b>. A host <b>31</b> may comprise a computer, workstation, server, virtual tape system, control unit, storage server, a storage control, a networked system, etc., as is known to those of skill in the art.

0036A robot control <b>33</b> may comprise a computer system, one or more processors, part or all of a distributed control system, FPGA (Field Programmable Gate Array), ASIC (Application Specific Integrated Circuit), discrete logic, or any other method of control as is known to those of skill in the art. A robot control <b>33</b>, in one embodiment, comprises a memory <b>34</b> to store the computer program code of a computer program product to cause the programmable computer system, processor, FPGA, ASIC or other programmable logic to provide the desired operations of the robot accessor <b>18</b>. The memory <b>34</b> may be integrated into a computer system, processor, FPGA, ASIC, or other device or system. Alternatively, the memory <b>34</b> may be a discrete memory or storage component. The memory may comprise electronic storage such as programmable logic, RAM (Random Access Memory), PROM (Programmable Read Only Memory), EEPROM (Electrically Erasable PROM), flash PROM, MRAM (Magnetoresistive RAM). Alternatively, the memory may comprise magnetic storage such as a hard disk drive, floppy drive, magnetic tape, etc. In addition, the memory may comprise optical storage such as an optical disk drive, optical tape, etc. Still further, the memory may comprise any memory or storage technology as is known to those of skill in the art. The computer program product may be supplied to the robot control <b>33</b>, for example, by means of the operator interface <b>23</b> or a web user interface. The computer program product may also be provided from some other user or remote interface, a network, host computer, library service port, through a wireless connection, or by a diskette, DVD (Digital Versatile Disk), memory card, or compact-disk “CD”, or any other method of providing a computer program product, as is known to those of skill in the art.

0037The robot control <b>33</b> is configured to operate the drive system, e.g. carriage <b>24</b>, to move the robot accessor <b>18</b>, and may operate the picker <b>20</b>.

0038In accordance with an embodiment of the present invention, the robot control <b>33</b> is configured to operate the bus bar relay <b>27</b>, either directly or indirectly, to engage the bus bar <b>28</b>, <b>29</b> when the robot accessor is stationary, and to disengage the bus bar <b>28</b>, <b>29</b> when the robot accessor is being moved. In a preferred embodiment, the bus bar relay <b>27</b> engages the bus bar <b>28</b>, <b>29</b> when there is no power present on robot accessor <b>18</b>, or the robot accessor stops due to a malfunction.

0039Referring to <figref idref="DRAWINGS">FIGS. 2A and 2B</figref>, the bus bar relay <b>27</b>, in one embodiment, comprises a pair of single pole single throw relays, comprising actuators <b>35</b> and <b>36</b> which operate communication arms <b>37</b> and <b>38</b> to move relay contacts <b>39</b> and <b>40</b> into engagement with the bus bar <b>28</b>, <b>29</b>, and to disengage the relay contacts. The bus bar <b>28</b>, <b>29</b> may be supported by frame support <b>41</b>, and communication bar <b>28</b> is insulated from the frame support.

0040In an alternative embodiment, the bus bar relay <b>27</b> may comprise multiple pole single throw contacts. Further, the bus bar relay <b>27</b> may comprise redundant relay elements to guard against single relay failure. Still further, the contacts may be sufficiently durable, for example, hardened contacts, so as to tolerate motion in contact with the bus bar <b>28</b>, <b>29</b> to allow for electrical contact during acceleration and deceleration of the accessor <b>18</b>, or in the event of a failure of actuators <b>35</b> and <b>36</b> or for long enough to allow the robot accessor to be moved out of the way along the rails for repair. In one embodiment, the actuators <b>35</b> and <b>36</b> are operated electrically in a similar way that a relay is actuated electrically. In another embodiment, the actuators <b>35</b> and <b>36</b> are operated through a mechanical link to the accessor drive or rail system. When the accessor <b>18</b> begins to move, the communication arms <b>37</b>, <b>38</b> are mechanically driven away from the bus bar <b>28</b>, <b>29</b>.

0041Referring to <figref idref="DRAWINGS">FIGS. 2A</figref>, <b>2</b>B and <b>3</b>, the robot accessor <b>18</b> comprises an accessor communication interface <b>43</b>. Wires <b>46</b> and <b>47</b> may provide a direct communication link between the relay contacts <b>39</b> and <b>40</b> and the accessor communication interface <b>43</b>. The wires <b>46</b> and <b>47</b> may be arranged to minimize the flexing of the wires to prolong their durability and reliability.

0042The robot control <b>33</b> is configured to operate the accessor communication interface <b>43</b> to provide communication capability with a library communication interface <b>48</b> via the bus bar relay <b>27</b> and the bus bar <b>28</b>, <b>29</b> when the bus bar relay <b>27</b> engages the bus bar <b>28</b>, <b>29</b>.

0043A library controller <b>50</b>, which may comprise one or more processors, may be in communication with the library communication interface <b>48</b>, and, when the communication capability is provided by the accessor communication interface <b>43</b> and bus bar relay <b>27</b>, the library controller <b>50</b> and the robot accessor <b>18</b> communicate in burst mode, for example, the library controller providing commands or signals to the robot control <b>33</b> to make desired moves, or providing address information so that a robot control <b>33</b> of the robot <b>18</b> can determine the desired moves. Additionally, the robot control <b>33</b> may provide information from the sensor <b>22</b> of <figref idref="DRAWINGS">FIG. 1</figref> mounted on the robot accessor or picker, such as information read from the shelves, markers within the library, and/or from labels of the data storage cartridges, and communicate the information to the library controller <b>50</b>. The accessor communication interface <b>43</b> and the library communication interface <b>48</b> may comprise a serial interface such as RS-232 (Recommended Standard), RS-422, CAN (Controller Area Network), USB (Universal Serial Bus), IEEE 1394, Ethernet, etc. Alternatively, the accessor communication interface <b>43</b> and the library communication interface <b>48</b> may comprise a parallel interface such as SCSI, IEEE 1284, etc. Still further, any commercial or proprietary communication interfaces may be use, as is known to those of skill in the art.

0044Herein, “communication capability” comprises any suitable operation which provides the ability to communicate via digital and/or analog signaling.

0045Referring to <figref idref="DRAWINGS">FIGS. 1</figref>, <b>2</b>A, <b>2</b>B and <b>3</b>, in a further embodiment, the automated data storage library additionally comprises a second communication system <b>30</b>, <b>53</b> between the robot accessor <b>18</b> and the automated data storage library, the second communication system operable at least when the robot accessor is moving.

0046The bus bar relay <b>27</b> is disengaged when the robot accessor <b>18</b> is moving, such that there is only burst communication when the robot accessor is stationary. The second communication system <b>30</b>, <b>53</b> may therefore serve in a low bandwidth communication mode as compared to the communication bandwidth of the accessor interface <b>43</b>, so as to be effective in a potentially high noise environment. The low bandwidth signaling may be as simple as a binary “on-off” coding, or more complicated coding or modulated signaling, and may comprise error correction techniques. An example of the signaling is that a constantly “on” signal from the robot accessor <b>18</b> indicates that the robot accessor is operating correctly, and/or moving, and an absence of a signal means that the robot accessor is experiencing trouble and/or is stopped. An example of signaling from the library to the robot accessor may be constantly “on” to indicate that the library is operating normally, and an absence of a signal means that power is about to go off. In one embodiment, the signaling from the library to the robot is used to indicate that it may not be safe for the robot to continue in motion. For example, a library access door <b>49</b> of <figref idref="DRAWINGS">FIG. 1</figref> may have been opened and continued robot motion may comprise a safety hazard for the person opening the library access door. In this example, the robot ceases any motion when the signaling from the library to the robot indicated that a library access door may have been opened. A library access door may comprise a door, hatch, cover, panel, magazine, or any other structure or assembly that may provide access to any portion of the library that is not normally accessible. Because of the possible noise, a threshold time period may be established for an absence of a signal to be registered by the receiver. Alternatively, a threshold in a coding or modulated signaling system may comprise a duplication of the signaling codes, or a special “attention” code sequence may be utilized, as is known to those of skill in the art.

0047Referring to <figref idref="DRAWINGS">FIGS. 1 and 3</figref>, in a further embodiment of the present invention, the robot control <b>33</b> is additionally configured to stop the robot accessor <b>18</b> if, while the bus bar relay <b>27</b> is disengaged, communication of the second communication system is lost for a predetermined threshold, the thresholds discussed above.

0048The example of a secondary communication system <b>30</b>, <b>53</b> illustrated in <figref idref="DRAWINGS">FIGS. 1 and 3</figref> comprises an RF (radio frequency) communication system, as is known to those of skill in the art.

0049<figref idref="DRAWINGS">FIG. 4</figref> illustrates an alternative secondary communication system comprising an optical communication system <b>55</b>, <b>57</b>, having an optical source <b>58</b>, <b>59</b>, and an optical receiver <b>60</b>, <b>61</b> at either side of the communication link, specifically at the robot accessor <b>18</b> and at the library communication interface <b>53</b>. The optical sources and receivers may comprise LEDs and optical detectors, and the LEDs may be provided throughout the library to provide communication with the robot accessor at all points in the library. Alternatively, the optical sources may comprise lasers. It should be noted that there may not be a need for two receivers <b>60</b>, <b>61</b> and/or two transmitters or sources <b>58</b>, <b>59</b>. This may be the case if there is only a need to determine library status or accessor status, and not both. In addition, there may not be a need for a secondary communication system at all. This may be the case if there are no safety concerns with a given library design. Still further, at the robot accessor <b>18</b>, the accessor sensor <b>22</b> may also serve as the optical communication system <b>30</b>. Further optical communication systems are also known to those of skill in the art.

0050Thus, the potentially noisy or intermittent nature of communication through RF or optical communications still is useable in the low bandwidth communication environment.

0051<figref idref="DRAWINGS">FIG. 5</figref> illustrates a further secondary communication system comprising a roller and bus communication system <b>67</b>, <b>68</b> employing rollers <b>70</b> and <b>71</b> of robot accessor <b>18</b> to contact the bus <b>28</b> and ground <b>29</b>, or a similar bus system, and to provide a low bandwidth communication, as discussed above, with respect to the library. Herein, such a system is termed a “bus bar contact”. The roller and bus communication system <b>67</b>, <b>68</b> is not well suited for high bandwidth communication during motion because the roller may induce noise, intermittent connections, etc. However, if high bandwidth communication is limited to periods where accessor motion is stopped, the roller and bus communication system <b>67</b>, <b>68</b> may be used as the primary burst communication instead of the bus bar relay. In one embodiment, the roller and bus communication system <b>67</b>, <b>68</b> actually provides the high bandwidth communication when the accessor is stopped. In a variation of this embodiment, a secondary communication system is used when the accessor is moving.

0052<figref idref="DRAWINGS">FIG. 6</figref> illustrates a further secondary communication system comprising a brush and bus communication system <b>75</b>, <b>76</b> employing brushes <b>78</b> and <b>79</b> of robot accessor <b>18</b> to contact the bus <b>28</b> and ground <b>29</b>, or a similar bus system, and to provide a low bandwidth communication, as discussed above, with respect to the library. Such a system is also termed a “bus bar contact”. The brush and bus communication system <b>75</b>, <b>76</b> is not well suited for high bandwidth communication during motion because the brush may induce noise, intermittent connections, etc. However, if high bandwidth communication is limited to periods where accessor motion is stopped, the brush and bus communication system <b>75</b>, <b>76</b> may be used as the primary burst communication instead of the bus bar relay. In one embodiment, the brush and bus communication system <b>75</b>, <b>76</b> actually provides the high bandwidth communication when the accessor is stopped. In a variation of this embodiment, a secondary communication system is used when the accessor is moving.

0053Thus, the intermittent nature of communication through rollers or brushes or similar bus bar contacts still is useable in the low bandwidth communication environment, and may even be used for high bandwidth communication when there is no motion.

0054Referring to <figref idref="DRAWINGS">FIGS. 2 and 3</figref>, a power supply <b>44</b> of the library may supply power (AC and/or DC) to the bus bar <b>28</b>, <b>29</b>. The power supply <b>44</b> comprises any suitable power supply as is known to those of skill in the art. A power storage system <b>45</b> is configured to receive power via the bus bar relay <b>27</b> when the bus bar relay engages the bus bar <b>28</b>, <b>29</b>. The communication signal may be modulated on the power signal. Alternatively, the communication signal may be capacitively coupled to the power signal. Still further, any method of combining power and communication signals may be used as is known to those of skill in the art.

0055Thus, both power and communications may be provided via the bus bar <b>28</b>, <b>29</b> and the bus bar relay <b>27</b> when the robot accessor is stationary and the bus bar relay engages the bus bar. Alternatively, there may be separate arms <b>37</b>, <b>38</b> and/or separate contacts <b>39</b>, <b>40</b> and/or separate bus bars <b>28</b>, <b>29</b> for communication and power.

0056The power storage system <b>45</b> may comprise a battery system, a capacitor system, and/or super-capacitor to store power, which systems are known to those of skill in the art. The power storage system <b>45</b> is arranged to receive power from the power supply <b>44</b> via the bus bar engaged bus bar relay, for example, by a direct connection to the relay contacts <b>39</b> and <b>40</b> via wires or cables <b>80</b> and <b>81</b> of <figref idref="DRAWINGS">FIGS. 2A and 2B</figref>. As discussed above, optionally, the bus bar may comprise one half <b>28</b> of the bus bar, and the ground connection may be provided through the contact of other metal parts.

0057The power supply system <b>45</b> stores the received power and may deliver the stored power to the picker <b>20</b>, the drive system, the accessor communication interface <b>43</b>, the bus bar relay <b>27</b>, the robot control <b>33</b>, <b>34</b>, to any secondary communication system <b>30</b>, and to any accessor sensor <b>22</b> of <figref idref="DRAWINGS">FIG. 1</figref>, if needed. Some or all of the components of the robot accessor <b>18</b> may receive power directly from the bus bar relay <b>27</b> or the bus bar contacts (<figref idref="DRAWINGS">FIGS. 5 and 6</figref>) when the robot accessor is stationary. In this case, the power supply system <b>45</b> may not be supplying any power while it is charging. Alternatively, the components of the robot accessor may always receive power from the power supply system <b>45</b>, even when the accessor is stopped. In this case, the power supply system <b>45</b> may be charging at the same time that is supplying power. The power is supplied at the desired voltages and current capacities and of the desired type (e.g. AC and/or DC), as is known to those of skill in the art.

0058The robot control <b>33</b> of <figref idref="DRAWINGS">FIG. 3</figref> may additionally be configured to determine if the bus bar relay <b>27</b> engages the bus bar <b>28</b>, <b>29</b>. For example, a detector <b>83</b> may sense the operation of the actuators <b>35</b>, <b>36</b> of <figref idref="DRAWINGS">FIGS. 2A and 2B</figref>, for example, by current flow, inductance, etc.; may sense the position of arms <b>37</b>, <b>38</b>, for example, by a micro switch; or may sense the completion of the circuit, for example, by voltage or signal. Examples of such detectors are known to those of skill in the art.

0059The robot control senses the condition of the detector <b>83</b> and, if the bus bar relay engages the bus bar, provides a signal via the accessor communication interface <b>43</b>, the bus bar relay <b>27</b>, and the bus bar <b>28</b>, <b>29</b> to indicate that the bus bar relay has engaged the bus bar. The library control <b>50</b> may receive and respond to the signal by activating the power supply <b>44</b>. Thus, power may be supplied only when the robot accessor <b>18</b> is stationary. The robot control <b>33</b> may also provide a signal to indicate that the bus bar relay <b>27</b> is to be operated to disengage the bus bar <b>28</b>, <b>29</b>. The library control <b>50</b> may thus deactivate the power supply prior to the disengagement and avoid surges to the system. This may limit the amount of pitting that may occur on the contacts and bus bar due to arcing or sparking and thereby improve bus bar relay contact life and/or bus bar life. Alternatively, robot control <b>33</b> and library control <b>50</b> may determine that the bus bar relay <b>27</b> has engaged the bus bar <b>28</b>, <b>29</b> by the fact that communication has been established on the bus bar, not requiring a detector <b>83</b>. A time delay and/or a communication signal between the robot control <b>33</b> and the library control <b>50</b> may be used by library control <b>50</b> as an indication that it can activate power to the bus bar. A communication signal between the robot control <b>33</b> and the library control <b>50</b> may also be used to indicate that power should be removed from the bus bar because the robot accessor <b>18</b> is about to move. Alternatively, since movement of the robot accessor is typically related to host or library commands, library control <b>50</b> may remove power from the bus bar prior to sending any commands or signals to robot control <b>33</b> that may result in robot accessor motion. These approaches may require that the robot accessor <b>18</b> has power to begin with. If the robot accessor <b>18</b> has run out of power, the library control <b>50</b>, or some other circuit coupled to the bus bar, may provide a detection method to allow the library control <b>50</b>, or other circuit, to determine that the bus bar relay <b>27</b> has made contact with the bus bar. Examples of how library control <b>50</b>, or some other circuit, may determine that bus bar relay <b>27</b> has made contact with the bus bar may comprise, measuring the impedance of the bus bar circuit, determining that an electrical load has been placed on the bus bar, determining that one or more circuits have been closed, etc. One skilled in the art will recognize that these methods may be employed with power circuits that do not require any actual involvement of library control <b>50</b>. Time delays may be employed to ensure that the contacts are not bouncing or in partial contact when power is applied to, or removed from, the bus bar. Herein, activating a power supply may comprise turning power on, or it may comprise an increase in voltage and/or current output of the power supply. Deactivating a power supply may comprise turning the power supply off, or it may comprise a decrease in voltage and/or current output of the power supply.

0060Those of skill in the art will understand that differing specific component arrangements may be employed than those illustrated herein.

0061While the preferred embodiments of the present invention have been illustrated in detail, it should be apparent that modifications and adaptations to those embodiments may occur to one skilled in the art without departing from the scope of the present invention as set forth in the following claims.